The Units of DNA Replication in Drosophila melanogaster Chromosomes

Abstract

The DNA which must be replicated in a chromosome of Drosophila melanogaster appears to exist as a single molecule of double-stranded DNA, which, for the largest chromosomes, has a length of about 2.1 cm, or 62,000 kb1 (Kavenoff and Zimm, 1973). We have studied both the topography of the units of replication in this chromosomal DNA and the rate of replication per unit in two different classes of Drosophila nuclei which exhibit very different S phases. Our purpose is to define the factors which determine the overall replication rate for these giant DNA molecules.